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Create Function Tool and Attach to Assistant

A 3-step recipe with Vapi. We can help you get access.

Recipe · 3 steps

Create Function Tool and Attach to Assistant

with Vapi

Create a function tool and bind it to an assistant via a model update.

  1. Create a custom function tool with a name, description, and a simple object parameter schema the assistant can fill in.
  2. Create the assistant that will later be given access to the tool.
  3. Update the assistant so its model references the function tool by id, attaching the capability to the existing assistant.
What you'll need to have ready
  • apiToken: Vapi private API key used as a Bearer token.
  • functionName: The name of the function the assistant can invoke.
  • functionDescription: A description telling the model when to call the function.
  • name: A human-readable name for the assistant.
  • firstMessage: The opening message the assistant speaks.
  • systemPrompt: The system prompt that shapes the assistant's behavior.
For your developer

Arazzo workflow vapi-ai:create-tool-attach-assistant, 3 operations: ToolController_create → AssistantController_create → AssistantController_update. Specs on APIs.io.

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